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Lennard-Jones PVT System Model

written by
Wolfgang Christian

The Lennard-Jones PVT System simulates a 2D system of particles confined between a thermal reservoir and a piston. This computer model is designed to study the equation of state for particles interacting via a simple but realistic molecular potential that has a weak long-range attraction and a strong short range repulsion. Slow-moving particles are color-coded as blue and fast particles are color-coded as yellow. Users can set the initial particle energy, the initial particle separation, and the thermal reservoir temperature Tr. The thermal conductivity parameter ? determines the probability that a collision with the thermal wall will affect (thermalize) the colliding particle. If the conductivity is one, the particle velocity after a reservoir collision is set according to Maxwell-Boltzmann statistics. If the conductivity is zero, all reservoir collisions are elastic and the total internal energy E of the system is conserved.

The piston input fields in the bottom panel are used to compress and expand the system. Users can approximate an adiabatic compression by setting ?=0 and can approximate an isothermal compression by setting ?=1. The piston speed must, of course, be small to insure that the system remains in equilibrium during the compression for a (quasi-static approximation) reversible process. Separate windows allow users to follow the change in state of the system on a PV plot or a time evolution plot.

The Lennard-Jones PVT model is a supplemental simulation for the article "Pressure Oscillations in Adiabatic Compression" by Roland Stout in The Physics Teacher 49(5), 280-281 (2011) and has been approved by the author and The Physics Teacher editor. The model was developed using the Easy Java Simulations (Ejs) modeling tool and is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_stp_md_LennardJonesPVTSystem.jar file will run the program if Java is installed.

Lennard-Jones PVT System Source Code
The source code zip archive contains an EJS-XML representation of the Lennard-Jones PVT System. Unzip this archive in your EJS workspace to compile and run this model using EJS.download 42kb .zip
Last Modified: March 12, 2011

Standards (2)

AAAS Benchmark Alignments (2008 Version)

4. The Physical Setting

4E. Energy Transformations

6-8: 4E/M4. Energy appears in different forms and can be transformed within a system. Motion energy is associated with the speed of an object. Thermal energy is associated with the temperature of an object. Gravitational energy is associated with the height of an object above a reference point. Elastic energy is associated with the stretching or compressing of an elastic object. Chemical energy is associated with the composition of a substance. Electrical energy is associated with an electric current in a circuit. Light energy is associated with the frequency of electromagnetic waves.

AAAS Benchmark Alignments (1993 Version)

4. THE PHYSICAL SETTING

E. Energy Transformations

4E (9-12) #2. Heat energy in a material consists of the disordered motions of its atoms or molecules. In any interactions of atoms or molecules, the statistical odds are that they will end up with less order than they began?that is, with the heat energy spread out more evenly. With huge numbers of atoms and molecules, the greater disorder is almost certain.

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